These vibrations, also known as clutch grabbing, can be self-excited or automatically excited. Self-excited clutch grabbing is caused by a drop of the clutch facing friction value in relation to the rate of sliding and can be rather considerable as a function of the power train overall damping.
Automatically excited clutch grabbing is in contrast stimulated by external sources in relation to the friction partners, including crankshaft axial vibrations or parallel deviations on the clutch pressure plate, in combination with an angular offset between the clutch pressure plate and the clutch disk that supports the friction lining.
The torsional vibrations that arise in the power train in connection with clutch grabbing are converted by the driven motor vehicle wheels into longitudinal oscillations of the entire motor vehicle and are transmitted via the service elements and via the motor vehicle seats to the motor vehicle occupants. Thus clutch grabbing is perceived by the vehicle passengers as unpleasant vibrations or oscillations that can also be associated with noise stress.
Although a high-level damping in the components of the power train does reduce the oscillation amplitudes with automatically excited clutch grabbing, this is nonetheless often an unrealistic demand due to the general wish for the lowest possible fuel consumption for a motor vehicle, since a permanently high damping in the power train is basically attainable only through a constantly active elevation of friction losses, for example in the transmission, in the bearings and in the seals.
Inserting a clutch friction lining with an increasing friction value curve over the rate of sliding has been proposed, for example, as a countermeasure for reducing clutch grabbing and the disturbing longitudinal oscillations of the motor vehicle that go along with it. The friction linings available at this time, however, are not capable of this.
Another possibility for reducing clutch grabbing consists in further reducing the manufacturing tolerances in the clutch region, however this would be possible only with a very high manufacturing expenditure, and it will produce a rather modest contribution to reducing clutch grabbing (“Grabbing-Causes and Remedies,” Prof. Albert Albers, Dr. Eng., Daniel Herbst, Cert. Eng. in: 6th LuK Colloquium, 1998).
Metrological recording of a clutch jerking in connection with a starting clutch or a converter bridging clutch by means of suitable sensors and a control and regulating device as well as active measures for ending this clutch jerking are moreover known from EP 845 616 A2. These measures consist of altering the ignition time of an internal combustion engine connected with the clutch via drive engineering in order thus to act upon the input torque into the clutch. Another measure provides for increasing the contact pressure of the clutch pressure plate on the clutch friction lining, whereby a slippage operation of the clutch offering some advantages is no longer possible.
Since the known measures bring on unsatisfactory results with respect to avoiding or reducing clutch grabbing, the object of the invention consists in presenting a method and device with which the disturbing rotational vibrations of the power train or the disturbing longitudinal oscillations can at least be diminished in their amplitude height.
The accomplishment of this objective is disclosed in the characterizing features of the method and device main claims, while advantageous further developments and refinements of the invention can be inferred from the dependent claims.